Warcraft bug with Adding items to sell to building.

When I remove an item and replace it by the same, but with more "charges", it removes one of the other item of the building, but sometimes only ...

Do u know a way to avoid this ?

I can send my map to someone who thinks he can fix this, it would be easier to do it this way :).

EDIT : I found how, I had to delete all items and add them all each time i wanna add 1 charge at 1 item :)